From 59f8ed6b3423efc893c752db80a066668b911d5f Mon Sep 17 00:00:00 2001
From: Dave Stevenson <dave.stevenson@raspberrypi.com>
Date: Wed, 8 Sep 2021 14:21:38 +0100
Subject: [PATCH] drm/panel/raspberrypi-touchscreen: Handle I2C errors.

rpi_touchscreen_i2c_read returns any errors from i2c_transfer,
or the 8 bit received value.
Check for error values before trying to process the data as
valid.

Signed-off-by: Dave Stevenson <dave.stevenson@raspberrypi.com>
---
 drivers/gpu/drm/panel/panel-raspberrypi-touchscreen.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

--- a/drivers/gpu/drm/panel/panel-raspberrypi-touchscreen.c
+++ b/drivers/gpu/drm/panel/panel-raspberrypi-touchscreen.c
@@ -297,13 +297,14 @@ static int rpi_touchscreen_noop(struct d
 static int rpi_touchscreen_prepare(struct drm_panel *panel)
 {
 	struct rpi_touchscreen *ts = panel_to_ts(panel);
-	int i;
+	int i, data;
 
 	rpi_touchscreen_i2c_write(ts, REG_POWERON, 1);
 	usleep_range(20000, 25000);
 	/* Wait for nPWRDWN to go low to indicate poweron is done. */
 	for (i = 0; i < 100; i++) {
-		if (rpi_touchscreen_i2c_read(ts, REG_PORTB) & 1)
+		data = rpi_touchscreen_i2c_read(ts, REG_PORTB);
+		if (data >= 0 && (data & 1))
 			break;
 	}
 
